The present invention relates to a black colorant for ink-jet printing ink, an ink-jet printing ink and an aqueous pigment dispersion containing the black colorant, and more particularly, to a black colorant for ink-jet printing ink exhibiting not only a high blackness and an excellent tinting strength, but also excellent dispersibility and light resistance in spite of fine particles; an ink-jet printing ink not only exhibiting excellent dispersion stability and light resistance, but also being free from clogging at a head portion of an ink-jet recording apparatus; and an aqueous pigment dispersion containing the black colorant.
In recent years, the development of various OA devices such as personal computers has rapidly spread in both business and domestic applications. An ink jet printer as one of recording apparatuses for these OA devices has also been widely used owing to the recent tendency of a low price and a high performance thereof.
Upon practical use, it is important that the ink jet printers have a higher reliability and a broader applicability.
To meet the requirements, ink-jet printing inks used in the ink jet printers have been required to be free from clogging at a head portion of the printers, and exhibit an excellent dispersion stability, a high print image density, excellent water resistance and light resistance, or the like.
Hitherto, various dyes have been used as black colorants for ink-jet printing inks because of nonoccurrence of clogging at a head portion of the printers, a good dispersion stability, a good chroma and a good transparency. However, these dyes have problems due to toxicity. In order to solve the problems as well as satisfy the recent requirement for light resistance of printed matters, it has been attempted to use pigments instead of the dyes. As to this fact, Japanese Patent Application Laid-Open (KOKAI) No. 11-131001(1999) describes that xe2x80x9c. . . Dyes have problems such as poor water resistance and light resistance of images printed therewith owing to inherent properties thereof. To solve the problems, it has been attempted to develop inks using pigments instead of the dyesxe2x80x9d.
When the black pigments such as carbon black, etc. are used as a black colorant for ink-jet printing inks, it is possible to form printed images having a high image density as well as excellent water resistance and light resistance as compared to in the case of using dyes as the black colorant. However, since 80% of the ink-jet printing inks are generally constituted of water, it has been difficult to disperse carbon black having a hydrophobic surface as well as organic black pigments in an aqueous medium. In addition, since the pigments are usually insoluble in water, etc., unlike the dyes, it has been difficult to preserve ink-jet printing inks using such pigments at a stable condition for a long period of time, and there arises such a problem that a head portion of an ink-jet recording apparatus tends to be clogged therewith.
On the other hand, if the particle size of the black colorant is reduced, it will be expected that the ink using such a black colorant can be prevented from clogging at the head portion, and can be improved in transparency. However, the black colorant having a small particle size tends to cause problems such as poor dispersibility in ink composition, low light resistance of ink using such a black colorant, or the like.
Conventionally, there are known ink-jet printing inks using pigments (Japanese Patent Application Laid-Open (KOKAI) Nos. 9-227812(1997), 11-131001(1999) and 2000-53901); colorants prepared by coupling pigments with resins particles using a coupling agent (Japanese Patent Nos. 2903631 and 3097208); and colorants prepared by bonding dyes onto the surface of silica particles through a coupling agent (Japanese Patent No. 3105511).
At present, it has been strongly required to provide a black colorant for ink-jet printing ink, which is not only excellent in tinting strength, light high blackness. However, conventional black colorants have still failed to satisfy these requirements.
That is, in Japanese Patent Application Laid-Open (KOKAI) Nos. 9-227812(1997) and 2000-53901, there is described an aqueous ink-jet recording liquid containing pigments and colloidal silica for the purpose of obtaining high-quality printed images. However, the pigments exhibit a poor dispersibility in an ink-jet printing ink composition, so that the resultant ink-jet printing ink fails to exhibit a good dispersion stability and a sufficient light resistance of printed images thereof. In addition, since a large amount of the colloidal silica not contributing to coloring is contained in the ink composition, it is difficult to sufficiently increase the pigment concentration thereof, thereby failing to obtain high-density printed images.
In Japanese Patent Application Laid-Open (KOKAI) No. 11-131001 (1999), there is described an ink-jet recording liquid containing pigments adhered with fine particles of silica or barium sulfate. However, since an adhesion force of the fine particles onto the surface of the pigments is very weak, the fine particles tend to be desorbed from the pigments when dispersed in the ink-jet printing ink composition, so that it has been difficult to obtain an ink-jet printing ink having excellent dispersion stability and anti-clogging property as well as excellent light resistance of printed images thereof.
In Japanese Patent Nos. 2903631 and 3097208, there is described an ink-jet printing ink, in which the particles prepared by reacting pigments and resin particles using a coupling agent are dispersed. Since the coupling reaction is conducted in a solution as shown in the below-mentioned Comparative Examples, a sufficient shear force cannot be applied to the pigments. Therefore, it is difficult to disperse the black pigments in the form of fine particles, thereby failing to uniformly adhere the pigments onto the surface of the resin particles.
In Japanese Patent No. 3105511, there are described particles prepared by adhering dyes onto the surface of silica particles through a silane-based coupling agent. As shown in the below-mentioned Comparative Examples, since the dyes are adhered onto the surface of silica particles, the obtained colored silica particles fail to show a sufficient light resistance.
Further, in Japanese Patent Application Laid-Open (KOKAI) Nos. 11-323174(1999) and 2001-11339, there are described iron-based black composite particles comprising black iron oxide particles or black iron oxide hydroxide particles; a coating layer formed on the surface of the black iron oxide particles or black iron oxide hydroxide particles, which comprises organosilane compounds obtainable from alkoxysilanes, or polysiloxanes; and a carbon black coat formed on the surface of the coating layer. However, as shown the Comparative Example mentioned later, since the iron-based particles as core particles have a specific gravity as high as 4.3 to 5.5 and the amount of the carbon black coat is not more than 30 parts by weight based on 100 parts by weight of the core particles, the obtained iron-based black composite particles have a high specific gravity. Therefore, it may be difficult to obtain an ink-jet printing ink having a sufficient dispersion stability when the iron-based particles are used as a black colorant therefor.
As a result of the present inventors"" earnest studies, it has been found that a black colorant having an average particle diameter of 0.001 to 0.15 xcexcm and comprising extender pigments as core particles, a gluing agent-coating layer formed on at least a part of the surface of the core particle, and a black pigment coat formed onto at least a part of the gluing agent-coating layer, exhibits not only a high tinting strength and a high blackness, but also excellent dispersibility and light resistance in spite of fine particles, and is suitably used as a black colorant for ink-jet printing ink. The present invention has been attained on the basis of the findings.
An object of the present invention is to provide a black colorant for ink-jet printing ink, in which black pigments are adhered onto the surface of extender pigment through a gluing agent in the form of a uniform adhesion coat while being kept in an extremely finely dispersed state, and which can exhibit not only a high tinting strength and a high blackness but also excellent dispersibility and light resistance in spite of fine particles.
Another object of the present invention is to provide an ink-jet printing ink exhibiting not only excellent dispersion stability and light resistance but also being free from clogging at a head portion of an ink-jet recording apparatus.
A further object of the present invention is to provide an aqueous pigment dispersion containing the black colorant for ink-jet printing ink.
To accomplish the aims, in a first aspect of the present invention, there is provided a black colorant for ink-jet printing ink, having an average particle diameter of 0.001 to 0.15 xcexcm, comprising:
extender pigments as core particles;
a gluing agent-coating layer formed on at least a part of the surface of the core particle; and
a black pigment coat uniformly formed on at least a part of said gluing agent-coating layer.
In a second aspect of the present invention, there is provided a black colorant for ink-jet printing ink, having an average particle diameter of 0.001 to 0.15 xcexcm, a BET specific surface area value of 15 to 1,000 m2/g, a specific gravity of 1.3 to 3.0 and a blackness L* value of not more than 22.0, comprising:
extender pigments as core particles;
a gluing agent-coating layer formed on at least a part of the surface of said core particle; and
a black pigment coat uniformly formed on at least a part of said gluing agent-coating layer in the amount of 1 to 500 parts by weight based on 100 parts by weight of said extender pigments.
In a third aspect of the present invention, there is provided a black colorant for ink-jet printing ink, having an average particle diameter of 0.001 to 0.15 xcexcm, comprising:
extender pigments as core particles;
a gluing agent-coating layer formed on at least a part of the surface of said core particle;
a black pigment coat uniformly formed on at least a part of said gluing agent-coating layer; and
an outer coating layer formed on at least a part of said black pigment coat, comprising at least one material selected from the group consisting of anionic surfactants, nonionic surfactants, cationic surfactants and polymeric dispersing agents.
In a fourth aspect of the present invention, there is provided a black colorant for ink-jet printing ink, having an average particle diameter of 0.001 to 0.15 xcexcm, comprising:
extender pigments as core particles;
a coating layer formed on at least a part of the surface of said core particle, comprising at least one compound selected from the group consisting of hydroxides of aluminum, oxides of aluminum, hydroxides of silicon and oxides of silicon;
a gluing agent-coating layer formed on at least a part of the surface of said coating layer;
a black pigment coat uniformly formed on at least a part of said gluing agent-coating layer.
In a fifth aspect of the present invention, there is provided a black colorant for ink-jet printing ink, having an average particle diameter of 0.001 to 0.15 xcexcm, comprising:
extender pigments as core particles;
a coating layer formed on at least a part of the surface of said core particle, comprising at least one compound selected from the group consisting of hydroxides of aluminum, oxides of aluminum, hydroxides of silicon and oxides of silicon,
a gluing agent-coating layer formed on at least a part of the surface of said coating;
a black pigment coat uniformly formed on at least a part of said gluing agent-coating layer; and
an outer coating layer formed on at least a part of said black pigment coat, comprising at least one material selected from the group consisting of anionic surfactants, nonionic surfactants, cationic surfactants and polymeric dispersing agents.
In a sixth aspect of the present invention, there is provided an ink-jet printing ink comprising an ink base solution and black colorant for ink-jet printing ink, having an average particle diameter of 0.001 to 0.15 xcexcm, comprising:
extender pigments as core particles;
a gluing agent-coating layer formed on at least a part of the surface of said core particle; and
a black pigment coat uniformly formed on at least a part of said gluing agent-coating layer.
In a seventh aspect of the present invention, there is provided an ink-jet printing ink comprising the black colorant as defined in any one of first to fifth aspects and an ink base solution
the amount of said black colorant being 1 to 20% by weight based on the weight of the ink base solution.
In an eighth aspect of the present invention, there is provided a aqueous pigment dispersion comprising a base solution for the aqueous pigment dispersion and 10 to 40% by weight of black colorant for ink-jet printing ink, having an average particle diameter of 0.001 to 0.15 xcexcm, comprising:
extender pigments as core particles;
a gluing agent-coating layer formed on at least a part of the surface of said core particle; and
a black pigment coat uniformly formed on at least a part of said gluing agent-coating layer.
In a ninth aspect of the present invention, there is provided an ink-jet printing ink comprising a dispersant, water and a aqueous pigment dispersion comprising a base solution for the aqueous pigment dispersion and 10 to 40% by weight of black colorant for ink-jet printing ink, having an average particle diameter of 0.001 to 0.15 xcexcm, comprising:
extender pigments as core particles;
a gluing agent-coating layer formed on at least a part of the surface of said core particle; and
a black pigment coat uniformly formed on at least a part of said gluing agent-coating layer.